A pressure-sensitive adhesive label can be used in many environments, e.g., it can be used as a merchandise display label to be stuck on a motor oil can, a kerosene can, it can be used as a label or emblem with characters printed thereon as gift to be attached to children's confectionery and it can be used as an air baggage tag. Such a label typically comprises a pressure-sensitive adhesive layer provided on a back side of a sheet such as pulp paper, aluminum foil, synthetic paper and a biaxially-stretched polyethylene terephthalate film and a release paper provided on the adhesive layer. Characters or images are printed or typed on a front side of the sheet as necessary.
As the release paper, there is often used a laminated paper comprising a pulp paper coated with a polyolefin resin film on one or both sides thereof, glassine paper, resin-coated paper and a release paper comprising a paper substrate coated with a release agent such as a silicone compound or a fluorine compound on one or both sides (front and back) thereof, or the like.
In applications requiring that the adhesive label has pencil writability or water proofness, a synthetic paper is used as the sheet material which forms the surface material as disclosed in JP-B-50-29738 (The term "JP-B" as used herein means an "examined Japanese patent publication"), JP-B-U-2-45893 (The term "JP-B-U" as used herein means an "examined Japanese utility model publication") and U.S. Pat. Nos. 3,963,851 and 5,318,817.
As such a synthetic paper there is used a microporous stretched polyolefin film obtained by stretching a polyolefin film such as polypropylene, polyethylene and polystyrene containing an inorganic fine powder such as calcined clay, calcium carbonate, talc, mica, titanium oxide and diatomaceous earth.
At present, pressure-sensitive adhesive labels comprising as a surface material the foregoing polyolefin synthetic paper which have been put into practical use are excellent in water proofness, abrasion resistance, printability and typability, but they have been recognized to tend to drastically curl at a temperature of 0.degree. C. or below, e.g., in the winter.
Such a pressure-sensitive adhesive label may not be able to be fed or discharged when it is subjected to printing or typing under a bad condition of 0.degree. C. or less. When one tries to stick such a pressure-sensitive adhesive label to an adherend (such as a container) by means of an automatic labeler under such low temperature conditions, when the release paper is peeled off the label, the synthetic paper curls more than it does in the Spring, Summer and Fall seasons. This causes the label to be stuck to the adherend in a position which deviates from the desired predetermined position. Therefore, the distance between the adherend and the label needs to be rather large, which slows the label sticking rate.
It has further been recognized that when used as a address printing label to be stuck on an envelope, such a pressure-sensitive adhesive label is liable to be misfed into or misdischarged from a printer, misarrangement on the envelope and misregistered printing.
The reason why such a polyolefin synthetic paper is curled more in the coldest season is believed to be that the release paper and the synthetic paper have different thermal expansion coefficients and the pulp paper which constitutes the release paper can shrink more easily when it is dried in the winter than in other seasons. Therefore, in order to minimize curling, procedures such as printing, typing and sticking should be carried out under the same condition as are encountered in Spring, Summer and Fall (10.degree. C. to 40.degree. C.). However, this is obviously impractical for all possible users.